1. Field of the Invention
The present invention relates generally to a speaker system, and more particularly to a speaker system capable of miniaturization, which is incorporated into hand-held, small-sized electronic equipment such as mobile telephones or PDAs (Personal Digital Assistants).
2. Description of the Related Art
Speaker systems are used in various apparatuses for the purpose of listening to music or diverse sound information. As used herein, the speaker system refers to a system including a speaker for directly outputting acoustic waves, and a peripheral device for regulating the output of the acoustic waves.
The speaker is arranged to generate acoustic waves from a sheet-like member such as cone paper or resin sheet, which oscillates in response to sound signals. When the sheet-like member oscillates, acoustic waves are output from its front surface and simultaneously acoustic waves of opposite phase thereto are output from its rear surface. When these acoustic waves reach a listener, wavelength components having a closer relation to opposite phases are more cancelled so that the sound pressure at that frequency will lower.
In order to solve such a problem, either of two techniques has hitherto been employed. One technique is to configure a speaker system by incorporating a speaker into a sealed enclosure such that only its front is open. This enables acoustic waves of opposite phase output from the rear of the speaker to be blocked. The other technique is to make up a speaker system by mounting the speaker itself on a flat board having a relatively large area. This imparts a sufficient distance to the acoustic wave path when the acoustic waves of opposite phase output from the rear of the speaker travel to the front, to thereby prevent any possible attenuation of acoustic waves of low frequency components.
In the former technique, it is necessary to render the enclosure making up the speaker system relatively large, resistant to oscillation and rigid. Accordingly, although the former technique may be suitable for the speaker system disposed in the room or the like, it may be problematic in terms of size and weight to incorporate the speaker system into the hand-held equipment.
The latter technique to mount the speaker on a relatively wide flat board also needs to incorporate such a wide flat board into the speaker system. Therefore, it is similarly difficult to incorporate the same into hand-held small-sized electronic equipment.
On the other hand, in the field of mobile telephones or PDAs for instance, receiving and reproducing music or melodies via a network such as Internet have become more and more active. In consequence, even a relatively small-sized speaker system tends to be subjected to an increasing demand for higher-quality sound reproduction.
It is therefore an object of the present invention to provide a speaker system capable of miniaturization and presenting a good sound quality.
Another object of the present invention is to provide a speaker system capable of miniaturization, taking the reproduction of low-frequency band into consideration.
According to an aspect of the present invention there is provided a speaker system comprising (i) an enclosure having an enclosure acoustic aperture formed at a predetermined position, for outputting acoustic waves to the exterior, and at least one opening through which acoustic waves are output, formed at another position different from the predetermined position of the enclosure acoustic aperture; (ii) a diaphragm disposed within the enclosure at a position confronting the enclosure acoustic aperture, for allowing acoustic waves of positive phase generated forwardly as a result of oscillations to be output through the enclosure acoustic aperture; a diaphragm holding member for peripherally holding the diaphragm in a freely oscillatory manner; (iii) a plate-like member arranged confronting and apart from a rear surface of the diaphragm; and (iv) a blocking member having at least one opposite-phase opening at a position relatively remote from the at least one opening, the opposite-phase opening acting as an opening for outputting therethrough acoustic waves of opposite phase generated by the diaphragm, the blocking member blocking the output of acoustic waves between the plate-like member and the diaphragm holding member, excepting the opposite-phase opening.
Thus, by providing the opposite-phase opening for delivering acoustic waves of opposite phase output from the rear surface of the speaker diaphragm, to a site within the enclosure relatively apart from the enclosure opening, the difference in path between the positive phase and the negative phase of acoustic waves is increased as much as possible so that the cancellations of the acoustic waves can be reduced. This enables even a relatively small enclosure to secure a good sound quality similar to a large enclosure.
An acoustic low-pass filter is preferably provided cooperatively by an air chamber defined by the plate-like member, the diaphragm holding member and the blocking member, and by the opposite-phase opening acting as exit for acoustic waves.
Thus, the air chamber defined by the plate-like member, the diaphragm holding member and the blocking member, and the opposite-phase opening acting as an exit for acoustic waves provide in cooperation an acoustic low-pass filter so that low tones can satisfactorily be reproduced.
Preferably, the enclosure is an enclosure for a mobile telephone, and the opening present in the enclosure is a card slot.
Thus, the enclosure can be one for a mobile telephone by way of example. The present invention is equally applicable to other small-sized enclosure for PDAs, etc., accommodating a speaker. Such small-sized apparatuses can typically have a card slot as an opening.
When the enclosure has a single opening, the opposite-phase opening may be arranged at a position remotest from the single opening of the enclosure.
Thus, if there is a substantially single opening in the enclosure, the opposite-phase opening would ideally be arranged at a position remotest from the enclosure opening in order to ensure maximal difference in path between the positive phase and the negative phase.
When the enclosure has a plurality of openings, the opposite-phase opening may be arranged at a position remotest from a major one of the plurality of openings, through which acoustic waves are output.
Thus, if there are a plurality of openings in the enclosure, it would be effective to arrange the opposite-phase opening at a position remotest from a major one of the plurality of openings, through which acoustic waves are output.
When the enclosure has a plurality of openings, the opposite-phase opening may be arranged at a position remote on average from a major one of the plurality of openings, through which acoustic waves are output.
Thus, if there are a plurality of openings in the enclosure, it would be effective to arrange the opposite-phase openings at a position remote on average from the plurality of openings.